The worst time I ever got stuck behind somebody in the checkout lane was a woman with her kid. She thought it would be cute to have her 3 year old give the clerk the $100 bill. The kid was acting really shy and wouldn't give the clerk the money. After about 5 minutes of coaxing the kid to give the money, the mom tried to get it.
Nope, the kid had the bill crumbled up in his hand and it was his, and he wasn't giving it up. The kid has a snow suit on, so he can squirm around. This goes on for another 5-10 minutes. Then we're back to trying to coax the kid to give the clerk the bill. The kid tosses the crumbled up bill. but nobody saw where it went, so now we're looking all over for it. Finally, it was found-then the clerk got the cash.